In a previous patent application of the same applicant, a valve or stopcock for fluids was proposed comprising a body, a swivel shutter in said body movable between a closed position and an open position, a control rod for said shutter, and a throttle or clamp lever keyed to said rod for the rotation of the shutter. The throttle or clamp lever is fastened axially on the rod by means of a lock screw that is tightened in a threaded hole envisaged at the top of the rod itself. In order to prevent uncontrolled disassembly of the throttle or clamp lever, the lock screw is configured to be tightened and loosened only by using a specific tool at the disposal only of whosoever is charged with managing the use or non-use of the valve to prevent tampering or frauds.
According to a preferred embodiment of this background invention, the lock screw has a polygonal head surmounted by a truncated-cone shaped dome, semi-spherical or of other shape, the base of which extends over the edge of the perimeter surface of the polygonal head, and the tool for turning said screw has at least two expansible elastic jaws to widen and extend in an axial direction the base extending over the dome on the head of the screw and then contractible to engage the perimeter surface of the polygonal head of the screw.
The putting into practice of the model presented here, however, has shown that with certain tools or utensils different from that envisaged, it is nonetheless possible, albeit with difficulty, to loosen the lock screw by locking onto the base of the dome that extends over the polygonal head.